1. Field of the Invention
The present invention relates generally to a method for repairing openings formed in and below sections of pavement, and more particularly to an immediate and permanent method for making such repairs.
2. Description of the Relevant Art
In the art of road (or pavement) making and repair, there is a universally acknowledged problem associated with the fact that utility companies are very often required to cut openings in roads, sidewalks, etc. so that they can insert (or fix defective) utility lines thereunder.
The problem with utility cuts is many fold. First of all, the utility companies, or the contractors they have hired, very often (at least 50% of the time) improperly restore the utility cuts after they have finished inserting or repairing the utility lines. This is primarily due to the fact that the utility companies or their contractors fail to follow the established engineering guidelines for backfilling the portion of the utility cut below the pavement with a granular backfill material. Normally, the utility companies fail to compact the backfill material to a sufficient degree (guidelines require that the material be compacted to at least 95% of its maximum unit weight), whereby the backfill material will settle over a period of time, creating relatively large voids between the backfill material and a pavement patch which has been placed thereover. This, in turn, leads to cracking, buckling and settling of the pavement patch, whereby it becomes difficult to travel on, and water is permitted to flow beneath the pavement where it does further extensive damage to surrounding subgrade (base) and pavement structure. Improper compaction is particularly prevalent with small utility repair cuts, i.e., less than 1.25 meters in width.
A second and related part of the problem is the fact that the utility companies and their contractors often fail to correct voids created below the pavement surrounding the utility cuts as a result of subgrade material falling away from the sides of the excavation. The accepted solution to this "overbreaking" problem is to cut back a portion of the pavement surrounding the original utility cut so that these voids are fully exposed and can be eliminated. However, the utility companies and their contractors often omit this important cutting back step because it is cheaper and easier for them to do so.
A third major part of the problem is the fact that after the backfill material has been inserted and compacted, the pavement (whether rigid concrete or flexible asphalt) above the backfill material is not permanently repaired. Rather, it is merely temporarily patched, such as with a "cold" asphaltic mixture, while a permanent patch is not made until several months later. Temporary patches are used primarily because backfilling materials do tend to settle to some degree (even if properly compacted) under the weight of the vehicles traveling over the pavement, and it is desirable to have the backfilling or subgrade materials completely settled before applying a permanent patch. Other reasons for temporary patching are (1) the fact that permanent patches cannot be made during the winter months or under severe weather conditions using conventionally available equipment, and (2) permanent (or hot) asphaltic materials are not available from asphalt manufacturers during winter months.
Unfortunately, temporary patches are of very low quality in comparison to permanent patches due to the fact that the temporary patch mixture fails to sufficiently bond to either the surrounding pavement or to itself. As a result, temporary patches become cracked, broken and eventually displaced under use, whereby they must be continually policed and often replaced (usually by local authorities) before the permanent patch is made. (It is not unusual to temporarily patch the same utility cut as many as 12 times during the course of a winter!) Thus, as the temporary patch degrades and becomes displaced, water, salt, etc. are permitted to freely flow into the utility cut where these elements do extensive damage to the surrounding subgrade and pavement structure.
The cost to every tax-paying, vehicle-driving person as a direct result of the overall utility cut problem is tremendous. For example, a study by the Army Corps of Engineers showed that ". . . on the average, streets without utility cut patching have a life of 20 years, whereas streets with utility cut patching have a life of 12 years." See an article entitled TRB Focuses on New Technology in the February 1986 issue of Better Roads Magazine pages 44 and 45. As a result of this shortened road life, new roads must be built prematurely. Premature road construction in the United States and Canada cost taxpayers several billion dollars annually. See for example a study entitled "Utility Cut Restorations Problems and a New Policy" published in April 1985 by the Metropolitan Toronto Roads and Traffic Department, wherein it is discussed that premature road construction in Toronto alone costs 3 million dollars annually. Additionally, utility cut restorations put a great financial burden on governments in the sense that they must continually police and do periodic maintenance on the restorations, either because the pavement patches are temporary (and expected to fail) or because of improper backfilling by the utility companies.
Furthermore, it has been shown that some local governments spend as much, if not more, in liability exposure due to the poor condition of roads (resulting to a substantial degree from the utility cuts) than they spend actually fixing the roads.
On a personal level, the maintenance costs of vehicles are increased, while the life expectancy of the vehicles is decreased, due to the utility cut problem. Also, the pavement defects resulting from utility cuts are a major public nuisance. "In addition to their visual appearance, depressions in the pavement due to settlement promote the ponding of water. The subsequent splashing of pedestrians and private property from passing vehicles results in cleaning bills, salt damage to plant life, and rust and rot damage to metal and wood fences and structures." See the Toronto study on utility cut restoration, discussed above.
In an effort to abate the first and second parts of the utility cut problem discussed above, some local governments have recently adopted the use of "unshrinkable fill" as a substitute for granular backfill materials. Unshrinkable fill is basically a weak, loosely-cemented, concrete material which can be poured in place. The material is self-compacting, and voids around the lip of an excavation caused by overbreaking are automatically force filled by the fluid nature of the material. Unshrinkable fill is at least as effective as properly compacted granular fill in providing a stable subgrade, and because it is loosely-cemented it can be easily excavated without mechanical assistance if future access to the buried utility lines is required. Under favorable conditions (sunny and warm), the unshrinkable fill sets up in as little as one hour, after which time a temporary patch is made in the pavement according to conventional practices. See the Toronto study on utility cut restoration. Temporary patches are used for substantially the same reasons as discussed above with respect to compacted, granular backfill, i.e., it is desired to wait for the filler material to completely settle before making a permanent patch, and it is often not possible to make permanent patches due to weather conditions.
This effort has been successful, but because it fails to address the entire utility cut problem, the third and very significant part of the problem remains.
Also, the fact that it takes at least one hour for the unshrinkable fill to set up is significant because the utility companies or their contractors making the repairs will not wait around during this time because it is prohibitively expensive to do so. Rather, metal or plastic sheets will be placed over the utility cut if the roadway in which the cut is made is required for immediate use, or the cut will be left open and barricaded if the roadway is not needed for immediate use.